Assessing in vitro methodologies for the determination of protein digestibility, amino acid digestibility, and protein quality

This study assessed the ability to determine in vitro protein digestibility (IV-PD) and amino acid digestibility (IV-AAD) in assessing protein quality using two in vitro static digestion models, the pH-drop and INFOGEST 2.0, on various plant-based samples. The pH-drop model was able to measure IV-PD directly for the calculation of in vitro Protein Digestibility Corrected Amino Acid Score (IV-PDCAAS), the official method in the USA/Canada. The INFOGEST 2.0 digestion products were analyzed by three different methods, including OPA derivatization, Kjeldahl, and individual amino acid analysis, to determine IV-PD. Only the amino acid analysis method offered the additional ability to determine IV-AAD and in vitro Digestible Indispensable Amino Acid Score (IV-DIAAS), the recommended method by the FAO/WHO. All four in vitro methods determined a wide range of IV-PD (65.2% to 100%) and IV-PDCAAS (0.30 to 1.12). The improvement of IV-PDCAAS by heat treatments was only observed by analyzing the INFOGEST products. All IV-PDCAAS strongly correlated with reported in vivo data, with a high R² value from 0.92 (amino acid analysis) to 0.96 (Kjeldahl method). Finally, to investigate the impact of using different protein quality assessments, all samples were categorized according to the respective protein content claims of each method. All four in vitro methods concluded similar claims for most of the samples by the PDCAAS, the DIAAS, and the PER (Protein Efficiency Ratio) – the official method in Canada, which agreed with in vivo data except for boiled wheat and chickpea. The PDCAAS method yielded higher protein content claims than the DIAAS and the PER methods. The present data demonstrated the potential of both in vitro digestion models in determining digestibility and protein quality, which could be applied as effective and sustainable non-animal alternatives for protein quality screening tools for researchers, industries, and consumers.